Looks like Portulaca to me, also known as Moss Rose. I don’t have any right now but have had them in the past and will get them again. They come in both single and double forms and oodles of both pastel and neon colours. They make a dazzling display when they all open up at once on a sunny day.

It’s an annual but self-seeds prolifically so once it’s been planted you can expect to have it for years, often appearing where it’s least expected like in the tiny cracks between pavers etc. It hasn’t much of a root system though so it can be easily eliminated if it pops up where it isn’t welcome.